The present invention relates generally to a motor vehicle, and control of a gear type transmission and, more particularly, to a new gearshift operation when another request for gearshift is made while a current gearshift operation is being carried out.
Developed in later years as a transmission for automobiles and other vehicles is an automated manual transmission including a friction clutch and a two-parallel-axis type transmission. This type of transmission is what is called a gear type automatic transmission. The gear type automatic transmission shares the same basic construction with the manual transmission. In the gear type automatic transmission, a hydraulically operated actuator or an electrically operated actuator is used for operating the friction clutch and performing gearshifts for eventually connecting or disconnecting torque between a prime mover and the transmission.
The gear type automatic transmission such as that described above includes no hydraulic clutch (a torque converter) interposed in a driving power transmitting system between the prime mover and a driving wheel. As compared with an automatic transmission using the torque converter, therefore, the gear type automatic transmission offers greater transmission efficiency and greater fuel economy. The gear type automatic transmission is also free from a slip feel that is unique to the torque converter, leading to improved drivability.
To accomplish a gearshift in the gear type automatic transmission, however, the friction clutch is temporarily released, during which a gear train forming a new gearshift position is properly selected. Because of this operation, there temporarily exists a torque interruption period, during which power generated by the prime mover is not transmitted to the driving wheel. This gives occupants of a vehicle a sense of discomfort as a gearshift shock. To solve this problem, proposed is a transmission that includes transmitting torque variable means interposed between an input shaft and an output shaft of the gear type automatic transmission (for example, Japanese Patent Laid-open No. 2000-65199). The transmitting torque variable means function to transmit torque while a gearshift is being carried out. Such an automatic transmission including the transmitting torque variable means can suppress torque interruption during the gearshift, offering outstandingly improved gearshift performance.
A gearshift control system for controlling the gear type automatic transmission as described above operates similarly to the automatic transmission with a torque converter as follows: Specifically, while the vehicle is running in an automatic gearshift mode, the gear type automatic transmission uses a previously set gearshift map as shown in FIG. 3. Then, a target gearshift position is calculated from an accelerator opening (an operated amount of acceleration means) that represents an amount of an accelerator pedal depression and a vehicle speed. The hydraulic or electric actuator is then operated to execute the gearshift to the target gearshift position. If a new gearshift command (a new gearshift request) is issued during the gearshift operation establishing the specified gearshift position, as through an operation by the driver to operate the accelerator pedal or the like, therefore, a renewed gearshift operation is to be executed as a result of the change in the target gearshift position.
If the transmission is forced into a renewed gearshift operation during a current gearshift operation, however, an attempt is made to release a friction element in a process of an engagement operation or to engage a friction element in a process of a release operation. This produces a sudden change in a rotating speed or an engagement capacity, resulting in a large gearshift shock. It then becomes inevitable to allow the gearshift operation to progress over an extended period of time so as to avoid the large gearshift shock. This presents a problem of a prolonged delay in gearshift response (gearshift time).